Re: [PATCH 3/5] md: Increase the frequency of recording checkpoint of recovery.

[NeilBrown <neilb@suse.de>]

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On Sat, 27 Oct 2012 10:28:20 +0800 majianpeng <majianpeng@gmail.com> wrote:

> With the hard disk capacity of larger,the entire recovery process
> becomes longer.So it should increase the frequency.
> Supposed the speed of recovery is 100MB/s(i think for HDD is good).
> The total time of recovery 4TB hdd is about 666 minutes.So change the
> frequency from 16 to 64 times,it's about 10mins.
> 
> Signed-off-by: Jianpeng Ma <majianpeng@gmail.com>
> ---
>  drivers/md/md.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index 01e25bd..ba328ee 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -7446,7 +7446,7 @@ void md_do_sync(struct md_thread *thread)
>  		if (!test_bit(MD_RECOVERY_RESHAPE, &mddev->recovery) &&
>  		    ((mddev->curr_resync > mddev->curr_resync_completed &&
>  		      (mddev->curr_resync - mddev->curr_resync_completed)
> -		      > (max_sectors >> 4)) ||
> +		      > (max_sectors >> 6)) ||
>  		     (j - mddev->curr_resync_completed)*2
>  		     >= mddev->resync_max - mddev->curr_resync_completed
>  			    )) {

I don't like this - the number '6' is completely arbitrary.

The original '4' was never about number of minutes.  It was a fraction of the
total effort needed.
I wanted to make sure you only repeated at most 10% of the required effort
(one order of magnitude).  >>4 is about 6% and easy to calculate.

If you want it to be about time (which I don't object to), then make it about
time.  Keep track of the last time we updated curr_resync_completed, and if
that is more than a few minutes ago, update it again.
This is what I said last time - if you want something to be based on time,
test the time.
If 'echo idle > sync_action' doesn't work (Which it seems it doesn't), then
it is OK to just do it in the kernel.

NeilBrown

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